The present invention relates to an operator cab arrangement for a mobile machine, and more particularly to a roll over protection structure for an underground mining machine.
Operator cabs for underground mobile mining machines have in recent times been strengthened to withstand the rigors of underground mining. For example, the roof and associated support members may be constructed to withstand occasional contact with the mine walls, as well as rock falls onto the roof of the cab, referred to as Falling Object Protection Structures (FOPS).
Machine owners or authorities have not generally seen the need to provide for roll over protection because of the confined spaces in which the machines work. Increasingly however, customers and statutory authorities have begun demanding Roll Over Protection Structures (ROPS) in the underground mining, exploration and tunneling industries, at least partly in recognition of the portion of the time during which the machines are operated above ground.
International ROPS Standards, such as ISO3471, SAEJ1040, AS2294.2, require that the cab withstand given lateral, vertical and longitudinal forces, as well as absorb a certain lateral energy. In a machine roll over, the energy absorbing criteria assists in slowing down the lateral rotation of the machine. Such absorption is also useful in reducing the forces transmitted to the mounts attaching the cab to the machine chassis, since an inflexible construction requires stronger mounts to prevent the cab from breaking loose from the chassis.
While underground machine cabs have been able to meet withstand the required forces via a relatively inflexible construction of the cab and chassis, the energy absorption goal has proven more difficult, due to the confined nature of the operating environment. A conventional ROPS for construction machinery, generally a rectangular tubular frame, may absorb lateral energy by bending at the corners, in the manner of a parallelogram. In order to minimize overall machine profile for operation in tunnels however, the cab of an underground machine generally has less space around the operator, and is mounted low to the ground alongside the bulk of the machine chassis. The cab consequently can not be constructed to bend as described above without intruding into a defined operator space or coming up against the machine chassis.
Kortelainen et al., in U.S. Pat. No. 5,799,746, issued Sep. 1, 1999, disclose an underground vehicle safety cab which with its frame and fastenings must independently withstand a given vertical loading. Lateral and longitudinal forces on the cab however, are transmitted to outside safety bars made of plates in the form of box girders, connected to the cab through reaction bars having flexible fixing elements. The flexible elements are simply rubber dampers which yield to their limit, after which the L-shaped safety bars can absorb a given lateral energy by bending at both a horizontal and vertical part.
The aforementioned construction is relatively complex and may have bending characteristics which are difficult to control or predict. What is needed is a simple mounting arrangement which provides the desired safety characteristics though controlled plastic deformation.
A roll over protection structure for a work machine includes an operator cab and a rotation mount connecting one face of the cab to the work machine. The rotation mount provides for pivotal rotation of the cab about an axis parallel to the work machine longitudinal axis. A deforming member connects a second face of the operator cab with the work machine and is characterized by elastic deformation responsive to normal operational shocks acting on said cab, and by controlled plastic deformation responsive to larger forces indicative of a machine roll over.